Magnetic film stacks are used in a variety of devices including Magnetic Random Access Memory (MRAM) devices. During manufacture, the magnetic film stacks are annealed in a thermal processor in order to achieve desired material properties.
FIG. 1 shows a prior art system 100 used for magnetic annealing of magnetic film stacks. The system 100 includes an annealing chamber 102 which is surrounded by a magnetic field generation component 104. The magnetic field generation component 104 may comprise a giant cylinder of ferromagnetic materials with coils to pass current therethrough in order to generate a magnetic field.
Heating elements 106 are located on the periphery of the heating chamber 102 to supply heat to heating chamber 102 during the thermal annealing process.
In use a plurality of wafers/substrates 108 with magnetic stacks for annealing are carried by a wafer carrier 110. The wafer carrier 110 is then placed in the annealing chamber 102 as indicated. The process of magnetic annealing includes heating the annealing chamber 102 to a temperature of between 200 to 600 degrees Celsius for anywhere between 30 minutes to 2 hours. The process may be carried out in a vacuum. Alternatively, the annealing chamber may be filled with a gas such as hydrogen, helium, argon, etc.
Current flowing through the magnetic field generation component 104 in the direction of the arrows 112 cause a magnetic field of between 1 to 5 Teslas to be induced within the annealing chamber 102.
The aforementioned magnetic annealing process suffer from the following disadvantages:                Conflicting requirements: For the best film crystallographic qualities large amounts of thermal energies are required to be supplied for a relatively long time (30 minutes to 2 hours. As a result some of the magnetic materials can start diffusing or moving thereby compromising device performance due to junction deterioration.        Long annealing times and higher temperatures affect the performance of the prefabricated silicon integrated circuits to which the magnetic stacks are integrated in a backend process.        The number of wafers that can be annealed per hour is small due to long annealing times.        Device performance may be compromised by reducing the annealing temperature and time to accommodate for the above problems.        The magnetic field is supplied by huge electromagnets that are very expensive and difficult to maintain. Complicated cooling systems are needed to keep the electromagnets cold. This increases the cost of manufacturing the magnetic film stacks.        The wafers are annealed as a batch of 25 or 50 and local thermal variations on a wafer are difficult to control; thermal radiation between each wafer further increases the temperature variations and hence the magnetic device performance.        Thermal variations are further aggravated by the gas flow dynamics if the wafers are annealed in gas ambience as the gas flow between the batch of wafers is not predictable and are subject to variations.        